Influence of mowing frequency on N competitions between plant and microorganisms of temperate grasslands under extreme summer droughts

Marco Tulio Lara-Jiménez1, Christina Bogner2
1 Ecological modeling Uni - Bayreuth
2 Ecological modeling, Uni-Bayreuth

P 3.5 in Droughts, floods and hidden flowpaths: This research holds WATER

Global warming is predicted to have large effects on local climatic events in Central Europe such as the occurrence of summer droughts during growing seasons. This could impact on the influence of mowing in the N distribution between plants and soil microbes. We test the effects of summer drought occurrence combined with mowing frequency on semi-natural grassland in southern Germany for one growing season to determine: changes in the N competition strength of plant and microorganisms, and changes in the soil N availability.

For these purposes we used a multifactorial experiment to quantify the fraction of inorganic N uptake by the plants and microorganisms after the application of a concentrated solution of labeled ammonium nitrate (N15H4-N15O3) in the upper soil. Extreme droughts were simulated at the early and late summer season with mowing regimes distributed in twice mowed and four mowed a year.

The main results were: The microbial biomass and microbial N did not differ significantly at different drought season occurrence. Mowing seems to have a positive impact on the microbial and plant biomass and on the N-status. Rapid microbial N-uptake: 10 - 20% already after 1 day, 20 - 30% after 4 days. Rapid N-inclusion in plants: 10 - 50% after 1 day. Late drought favors N-inclusion in plants, much more than early drought.

Our preliminary conclusions are: mowing frequency and extreme drought had positive N-inclusion for plants, improving the N-supply after mowing (less biomass and higher N-inclusion). Adaptation strategies of microorganisms improve N-supply at short term. In general, mowing frequency is a good management strategy to increase microbial adaptation, which in turn improves plant adaptation to extreme drought.

Keywords: Key words: climate variability; mowing frequency; summer drought; plant and microbial biomass; N15; N-inclusion; N-uptake.
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